Half-bridge temperature compensating deflection sensor



June 4, 1963 P. BECKMAN 3,092,798

HALF-BRIDGE TEMPERATURE COMPENSATING DEF'LECTION SENSOR Filed July l0, 1961 zok/ 1N V EN T OR. Pa u/ Beckman BY f /l for/7@ Patented June 4, 1963 3,092,798 HALF-BRIDGE TEMPERATURE COMPENSATING DEFLECTION SENSOR Paul Beckman, 944 Henrietta Ave., Huntington Valley, Pa. Filed July 10, 1961, Ser. No. 122,848 Claims. (Cl. 338-2) This invention relates to bonded electrical resistance filament-type strain gages that are especially adapted to high temperature operation.

It is an object of my invention to provide an improved gage of this type that is so constructed and arranged that it can be manufactured relatively economically 1n sub-miniaturized form while still obtaining a necessary degree of accuracy and sensitivity combined with relative ruggedness for a device of such minute size.

Other objects and advantages will be more apparent to those skilled in the art from the following description of the accompanying drawings in which:

FIG. l is a greatly enlarged longitudinal sectional View of one form of my improved gage; FIG. lA is an enlarged detail of a modified terminal end of the gage of FIG. l;

FIG. 2 is a T-frarne of modified form of gage;

FIGS. 3 and 3A respectively show strain gage and temperature compensating filament and lead units, per se, ofthe FIG. 2 form of gage;

FIGS. 4 and 4A show the successive steps by which the temperature compensating filament is supported in an untaut state; Y 4

FIGS. 5 and 5A show respectively the temperature compensating filament and strain-sensing filament with their leads at one end bent preparatory to being ass-embled on the T-frame of FIG. 2.

FIG. 6 shows the fully assembled and completed gage made from the parts shown in FIGS. 2 to 5A.

In FIG. 1 I have shown a T-shaped metal frame consisting of a center tube 1 and a lateral terminal in the form of a cross tube 2 secured to the center tube by silver soldering 3 or by spot welding. This center tube serves not only as the main frame member but also as the center electrical lead. A strain-responsive electrical resistance filament 4 has one end inserted into the tubular terminal 2 which is thereupon swaged fiat to pinch the filament for holding the same. The Iother end of the filament is similarly inserted in a metallic tubular lead 5 and held thereto by swaging the end 6. A similar strain responsive filament 7 is secured in the other end of the cross terminal 2 and to a lead 8. In this particular form of gage it is desirable to have the two filaments substantially equally spaced from and parallel to the longitudinal axis of the gage which in this case would be the axis of tube 1 and also to provide an insulator that will prevent any possibility of the filaments being electrically shorted by contacting the metallic center tube. l accomplish this by providing a tube of insulation 11 enclosing the tubular lead 1 from a point adjacent the cross terminal 2 to a point 12 preferably beyond the other end of the filament, while the desired uniform spacing of the filaments at the lead end of the gage is obtained by insulating tubular spacers 13 and 14 through which the laterally disposed leads 5 and 8 extend. These spacers are practically in contact with center insulating tube 11 and are of such size that the filaments 4 and 7 are positioned substantially parallel to each other and to the gage axis. All insulator tubes are preferably made of silica. The entire structure thus far described is enveloped or encased in a coating of usual ceramic cement 15 that covers and thus binds together portions 16 of all leads so that everything is firmly fixed together. If desired, the cross terminal 2 of FIG. l may have its ends bent as at 17, FIG. lA, to receive the filaments 4 and 7 without requiring such filaments to be bent at right angles as shown in FIG. l.

A gage ofthe type shown in FIG. l may perform the function of determining bending strains in any desired structure simply by placing the longitudinal axis of the gage on the neutral axis of the structure with the filaments disposed on the opposite side of such axis so that the filaments are respectively subjected to tension and compression during bending. With the three leads 1, 5, and 8 connected in adjacent arms of a bridge the electrical outputs `off the two filaments when subjected to tension and compression strains is additive as Well as affording temperature compensation. The construction of this gage with the relatively strong T-frame type of center lead is highly conducive to providing a rugged sub-miniaturized gage as well as insuring a relatively economical construction for manufacture. The filaments 4 and 7 are preferably of Well-known electrical strainsensitive wire although obviously such filaments may have different cross-sectional configurations such as being flat in case the filaments are made -ot well-known foil. The gage shown in FIG. l is not, of course, limited in its use for determining bending strains as it can be laid on the surface of a test specimen for determining tension or compression strains therein. The gage assembly is, of course, cemented to the test specimen in the usual and well-known manner by using usual ceramic cements for high temperature application.

The gage shown in FIG. 5` is of the half-bridge configuration, as is also broadly the case with FIG. l. However in FIG. l if a gage is used for measuring just tension (or compression) strains, there is no temperature compensation, whereas in FIG. 6 temperature compensation is obtained by having a strain-responsive filament 24) and an untaut temperature compensating filament 2l. The construction of this gage broadly includes the smc T-type frame consisting of a metallic center tube lead 22 preferably liattened throughout its length and a laterally extending -cross terminal support 23 welded, silver soldered, or otherwise secured to the end Iof the center lead 22. The two filaments 20 and 21 are of the same length as shown in FIGS. 3 and 3A and the ends of each are inserted in tubular leads 24, 2S, 26 and 27 whose ends are then swaged fiat to hold the filaments. To produce the untaut -condition of filament 21 the lead 26 is passed through a tube of insulation 28 preferably of silica and secured thereto near one end of the filament by a cap of ceramic cement 29. The insulator tube 28 is sufficiently shorter than the filament so that upon inserting the lead 27 into the end of insulator tube 28 the lament 21 takes an untaut wavy condition. The lead 27 and tube 28 are then secured together by a ceramic cap 29. In the next step as shown in FIGS. 5 and 5A the terminals 24 and 26 are reversely bent as at 31 and 32 preferably at a slight angle as shown. These bent leads are then hooked over the cross terminal support 23 and welded or otherwise suitably secured thereto as shown in FIG. 6. The bent ends 31 and 32 may then be cut ofi if desired. The leads 25, 27 and 22 are then held in spaced relation as shown while a ceramic coating 34 completely encases the entire structure.

It will, of course, be understood that various changes in details of construction and arrangement of parts may be made by those skilled in the art without departing from the spirit of the invention as set forth in the appended claims.

I claim:

l. An electrical resistance-type strain gage having a frame comprising a longitudinally extending metallic center lead and a separate metallic frame member mechanically and electrically connected to one end of the center lead and extending laterally thereof, said lateral frame having a tubular portion extending along one side tot the center lead substantially in the same longitudinal direction as the center lead, an electrical strain-responsive filament connected directly into said axially extending tubular portion and extending substantially parallel to said center lead, a lead connected to the other end of said filament and being disposed adjacent to said center lead, and a casing of cement enveloping the filament and leads to hold them together as a unit.

2. A strain gage comprising a longitudinally extending metallic center lead, a cross member secured to oneend of said center lead to form a T-shape frame, a pair of filaments disposed substantially parallel to said center lead on opposite sides thereof and connected at one of their ends to said cross member, leads connected to the other ends of said filaments and disposed adjacent to and laterally of the center lead, said cross member being of tubular form into Whose ends the filaments are disposed and held therein, an insulator tube extending over said center lead from the cross member to the adjacent portions of the other leads, and a ceramic coating covering the cross member, filaments and leads to form a unitary structure.

3. A strain gage -comprising a longitudinally extending metallic center lead, a cross member secured to one end of said center lead to form a T-shape frame, a pair of filaments disposed Substantially parallel to said center lead on opposite sides thereof and connected at one of their ends to said cross member, leads connected to the other ends of said filaments and disposed adjacent to and laterally or" the center lead, said cross member being of tubular form into Whose ends the iilaments are disposed and held therein, an insulator tube extending over said center lead from the cross member to the adjacent portions of the other leads, tubular spacers disposed over said adjacent portions of said other leads to maintain them a predetermined distance from the center lead so that the filaments are substantially parallel to each other, and said coating of insulation extends entirely over said spacers and over a portion of the center lead adjacent to said spacers as well as over a portion of the lateral leads, and a ceramic coating covering the cross member, filaments and leads to form a unitary structure thereby to form a unitary structure.

4. A strain gage comprising a longitudinally extending metallic center' lead, a cross member secured lto one end of said center lead to form a T-shape frame, a pair of iilaments disposed substantially parallel to said center lead on opposite sides thereof and connected at one of their ends to said cross member, leads connected to the other ends of said filaments and disposed adjacent to and laterally of the center lead, said center lead and cross member being of tubular form and the ends of the cross member are ben-t to extend in the same direction as the longitudinal axis of the center lead and toward the leads at the other end of the center lead so that the ends of the iilaments extend along a straight line into such lbent ends of the cross member, and a ceramic center covering the cross member, filaments and leads to form a unitary structure.

5. The combination set forth in claim 2 further characterized by the provision of a terminal connected to the ends of the filament adjacent to the T-shape frame, and said terminals being reversely bent over the cross-member of the T.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ELECTRICAL RESISTANCE-TYPE STRAIN GAGE HAVING A FRAME COMPRISING A LONGITUDINALLY EXTENDING METALLIC CENTER LEAD AND A SEPARATE METALLIC FRAME MEMBER MECHANICALLY AND ELECTRICALLY CONNECTED TO ONE END OF THE CENTER LEAD AND EXTENDING LATERALLY THEREOF, SAID LATERAL FRAME HAVING A TUBULAR PORTION EXTENDING ALONG ONE SIDE OF THE CENTER LEAD SUBSTANTIALLY IN THE SAME LONGITUDINAL DIRECTION AS THE CENTER LEAD, AN ELECTRICAL STRAIN-RESPONSIVE FILAMENT CONNECTED DIRECTLY INTO SAID AXIALLY EXTENDING TUBULAR PORTION AND EXTENDING SUBSTANTIALLY PARALLEL TO SAID CENTER LEAD, A LEAD CONNECTED TO THE OTHER END OF SAID FILAMENT AND BEING DISPOSED ADJACENT TO SAID CENTER LEAD, AND A CASING OF CEMENT ENVELOPING THE FILAMENT AND LEADS TO HOLD THEM TOGETHER AS A UNIT. 